1. Field of the Invention
The present invention relates to a process for producing a bumper for a vehicle and particularly, to an improvement in a process for producing a bumper for a vehicle, which is made of a synthetic resin and has a sandwich structure including a core and an outer layer covering the core, the process including a first step of injecting an outer layer forming material into a bumper forming cavity through a gate in a mold, and a second step of injecting a core forming material, thereby allowing the core forming material to flow into the outer layer forming material existing in the gate and cavity, while allowing the outer layer and core forming materials to flow within the cavity.
2. Description of the Related Art
In such a conventional bumper, the thickness thereof is set such that it is relatively thin and substantially uniform in its entirety, and a mounting portion for mounting to a vehicle body to extend laterally from a central portion of the vehicle body forms a rear edge of a front and upper portion of the bumper. In this case, a gate opens into a mounting portion forming area of the bumper forming cavity in the mold.
In the process for producing the bumper, while the outer layer forming material is flowing within the cavity, the core forming material is allowed to flow into the outer layer forming material. However, after a front portion of the outer layer forming material in a flowing direction has reached to a terminal end of the cavity to stop its flowing, it is difficult to allow the core forming material to flow into the front portion of the outer layer forming material in the flowing direction.
In an attempt to produce a bumper using the mold under such a situation, when the outer layer forming material is injected into the cavity, the capability to distribute the material into the mounting portion forming area in a lengthwise direction of the cavity (in a lateral direction of the vehicle body) is low due to a small volume (i.e., a narrowness) of the mounting portion forming area. For this reason, as compared with the time taken for the outer layer forming material to reach a central end area of the cavity nearer to the mounting portion forming area to stop its flowing, the time taken for the outer layer forming material to reach lengthwise opposite end areas remoter from the mounting portion forming area to stop its flowing is remarkably long. As a result, in the central end area, the core forming material fails to flow into the outer layer forming material. Due to this, it is impossible to produce the bumper having a sandwich structure in its entirety.